1. Field of Invention
This invention relates generally to intravascular stents, and more particularly to intravascular stents that include a plurality of cavities formed on a surface of the stent and are coated with a restenosis inhibiting agent.
2. Description of the Related Art
By 1999, the percutaneous balloon angioplasty and stent implant procedures have become the dominant non-surgical revascularization method of the atherosclerotic stenosis, or obstruction, of the vascular lumen, and particularly in the coronary vascular system in the heart. With balloon angioplasty alone, without use of stent, the restenosis rate after angioplasty has been as high as 25-45% in the first time clinical cases. With use of stents after balloon angioplasty, the restenosis has been reduced significantly. Even so, the restenosis rate after stent implant is reported as 10-25% range depending on the condition of the vessel stented or what specific stent was used, requiring a need for further restenosis reducing measures after intravascular stenting.
To further reduce the restenosis rate after stent implant, numerous means has been tried, including laser, atherectomy, high frequency ultrasound, radiation device, local drug delivery, etc. Although the brachytherapy (radiation treatment) has proved to be reasonably effective in further reducing restenosis after stent implant, using brachytherpy is very cumbersome, inconvenient and costly. Mainly because it is radioactive device and radiation therapy specialist from another department has to be involved with the interventional cardiologist in the cardiac catheterization laboratory. The laser and atherectomy devices proved to be marginally useful in this purpose with added costs.
The local drug therapy appears be a very promising method for the future, as better pharmaceutical, chemical or biogenetic agents are developed and became available. Some research data, both from animal tests and human clinical studies, indicate that there are evidences of suppressing restenosis after stent implant when certain growth blocking pharmaceutical agents available today are used to coat the stent. In another instances, it has been speculated that certain surface modifying materials coated on the surface of the stent may be beneficial by it alone or in combination with growth suppressing agent, in reducing restenosis rate. In either instance, the drug or substance should be locally attached or coated on the stent and in sufficient amounts. However, attaching or coating a sufficient amount of a substance or drug on the coronary stent is not so easy a proposition.
Coating a drug or an agent on the surface of the stent has a demanding problem of enough volume of such substance coated on the small surface areas of stent struts, without increasing the physical width or thickness of stent struts. This demand directly conflicts with the metal fraction issue of the stent. If the width (and lesser degree the thickness) of stent struts is increased in order to widen drug coating surface areas, it would have an elevated deleterious foreign body effect of the increased metal fraction of the stent, which would promote restenosis.
Designing an ideal stent, particularly the coronary stent, is a very demanding balance of a numerous conflicting factors. An ideal stent requires an ideal balance of numerous different stent features built into the stent. One of the many requirements of a coronary, or any vascular stent, is to keep the metal fraction of the stent low. This means that drug coating is a very demanding task. Enough amounts of a drug or agent should be coated on the miniscule surface areas of the stent struts, in order to have the desired drug results of reducing restenosis. An average stent, particularly a coronary stent, will have problem of providing desired amount of drug-retaining capacity on the surface areas of the stent struts.
The main invention of this application is not an invention of the stent itself. The present invention is the particular measures designed to increase drug coating or attachment capacity of a stent by adding exposed surface areas or reservoir capacity of the stent, without increasing the width or thickness of the stent struts or without increasing the metal fraction of the stent. These special measures of present invention will enhance the coating substances to a stent. Further, the present invention will enhance the reservoir capacity of the stent for different forms of restenosis reducing proteins, chemicals or drugs, and will prolong the releasing time duration of the substances.
U.S. Pat. No. 6,190,404 discloses an intravascular stent with an outer surface, an inner surface and grooves formed in the inner surface of the stent. The grooves are positioned and provided to increase the rate of migration of endothelial cells upon the inner surface of the stent.
There is a need for a stent with a geometry that provides for an increased amount of a coating substance. There is a further need for a stent that includes reservoirs for retaining coatings.
Accordingly, an object of the present invention is to provide an intravascular stent with a geometry that provides for an increased amount of a coating substance. Another object of the present invention is to provide an intravascular stent with cavities formed in the stent that serve as reservoirs of coatings applied to the stent. Yet another object of the present invention is to provide an intravascular stent with cavities formed in the body of the stent and with a restenosis inhibiting agent applied to the stent.
Another object of the present invention is to provide an intravascular stent with micro-holes or micro-slits that provide reservoirs for stent coatings. These and other objects of the present invention are achieved in an expandable stent. A tubular structure includes an outer surface positionable adjacent to a vessel wall and an inner surface facing a lumen of a body passageway. The tubular structure further includes a plurality of expansion struts, connector struts and cells. The tubular structure has a first diameter which permits intraluminal delivery of the tubular structure into the body passageway, and a second expanded and deformed diameter which is achieved upon the application of a radially, outwardly extending force. A plurality of cavities are formed in the outer surface of the stent.
In another embodiment of the present invention, an expandable stent, includes a tubular structure with an outer surface positionable adjacent to a vessel wall, an inner surface facing a lumen of a body passageway, a plurality of expansion struts, connector struts and cells. The tubular structure has a first diameter which permits intraluminal delivery of the tubular structure into the body passageway, and a second expanded and deformed diameter that is achieved upon the application of a radially, outwardly extending force. A plurality of cavities formed in the outer surface of the stent. A coating substance is on at least a portion of outer surface of the stent including and extends into at least a portion of the cavities.
In another embodiment of the present invention, a stent assembly includes a balloon and an expandable stent positioned at an exterior of the balloon. The stent includes a tubular structure with an outer surface positionable adjacent to a vessel wall, an inner surface facing a lumen of a body passageway, a plurality of expansion struts, connector struts and cells. The tubular structure has a first diameter which permits intraluminal delivery of the tubular structure into the body passageway, and a second expanded and deformed diameter that is achieved upon the application of a radially, outwardly extending force applied by the balloon. A plurality of cavities are formed in the outer surface of the stent. A coating substance is on at least a portion of outer surface of the stent including and extending into at least a portion of the cavities.
In another embodiment of the present invention, a method of manufacturing an intravascular stent is provided. The intravascular stent has an inner surface and an outer surface. A plurality of cavities are formed on the outer surface. A coating substance that inhibits restenosis is formed on at least a portion of the outer surface and on at least a portion of the plurality of cavities